SWEET-CLOVER SEED. 
21 
Table VII. — Influence of the weather at blossoming time upon the yield of sweet -clover 
seed, at Ames. Iowa, in 1915. 
Date, 
1915. 
Weather conditions. 
Insect visitors. 
Number 
of 
flowers 
that 
opened. 
Pods 
formed. 
Percent- 
age of 
flowers 
that 
matured. 
Aug. 16 
Aug. 17 
Aug. 18 
Aug. 19 
Aug. 20 
Aug. 21 
Aug. 22 
Aug. 23 
Aug. 24 
Cloudy and showery 
Rain all day 
Cloudy most of the day. . . 
, Clear and cool 
! Mostly clear and warm . . . 
Clear and warm 
Partlv cloudv and warm. 
....do : 
Cloudy till mid-afternoon. 
Very few. . 
None 
Very few. . 
Numerous. 
....do.... 
do. 
k...do. 
Few... 
102 
69 
60 
94 
61 
81 
181 
37 
18 
4 
20 
53 
38 
44 
100 
12 
17.6 
5.7 
33.3 
56.3 
62.2 
54.3 
55.2 
32.4 
The data given in Table YII show that the percentage of effective 
pollination is much higher in clear weather, when insects are active, 
than in cloudy or rainy weather, when but few insects visit the 
flowers. 
INSECT POLLINATORS OF SWEET CLOVER. 
On account of the ease with which the heavy flow of nectar of 
sweet-clover flowers may be obtained many insects visit the flowers, 
thereby pollinating them. While the useful insect visitors of flowers 
of red clover are limited to a few species of Hymenoptera, those 
pollinating sweet-clover blossoms are many and belong to such 
orders as Coleoptera, Lepidoptera, and Diptera, as well as to the 
Hymenoptera. However, in the United States the honeybee is the 
most important pollinator of sweet clover. In many parts of the 
country the different species of Halictus, co mm only known as sweat 
bees, rank next in importance. The margined soldier beetles 
(Cf'tauliognutlius marginatus Fabr.) were very active pollinators at 
Arlington, Va., in the latter part of June and first part of July, 1916, 
but the woolly bear (Diacrisia virginica Fabr.) was the only night- 
flying insect found working on sweet clover at Arlington. 
Insects belonging to the genera Halictus, Syritta, and Paragus 
were very active pollinators at Ames, Iowa, in 1916, and ranked 
next in importance to the honeybee. In fact, the results obtained 
in the cage where the plants were protected from visitation by 
insects that could not pass through a screen having II meshes to 
the linear inch showed that these small insects were able under 
the conditions of that experiment to pollinate practically as many 
flowers as larger insects. 
The insects listed below were collected while visiting Melilotus 
alba and M. officinalis flowers in 1916. 
